1. Field of the Invention
This invention relates to metallic seals and, in particular, to a stackable metallic seal and a method of using same.
2. Description of the Related Art
In many industries, such as the oil and gas industry, it is often necessary to provide reliable fluid seals in extremely hostile environments. For example, the flow control equipment associated with oil and gas wells (e.g., Christmas trees, valves, connectors, and the like) are provided with a large number of seals that isolate the produced fluids and control fluids (e.g., hydraulic fluid, methanol, and the like) from the environment. Such seals are often made of nonmetallic, elastomeric materials.
One conventional configuration for elastomeric seals is a U-type or V-type arrangement, wherein a plurality of “U” or “V” cross-sectionally shaped seal elements are stacked in such a way that the sealing lips of one element are energized by the axial force exerted by the adjacent element. Several embodiments of this type of seal are shown and described in commonly owned U.S. Pat. No. 4,576,385 to Ungchusri et al., the entirety of which is hereby incorporated by reference for all purposes.
In many wells, however, the produced fluid exits the well at very high temperatures and pressures. Nonmetallic seals may extrude and mechanically degrade under these conditions, ultimately leading to failure of the seal. There is also a risk of fire in oil and gas wells, which can damage or destroy such nonmetallic seals.
One way of addressing these problems is to use metal-to-metal seals, rather than nonmetallic seals, in portions of the equipment that are subject to high pressure and/or high temperature conditions. One type of metal-to-metal seal is known as a straight bore metal seal, which comprises a mechanically-energized sealing lip that seals against a generally smooth, cylindrical surface. Several embodiments of this type of seal are shown and described in commonly-owned U.S. Pat. No. 4,471,965 to Jennings et al., the entirety of which is hereby incorporated by reference for all purposes.
Such straight bore metal seals are generally effective when the surface against which the seal contacts is smooth. However, if the surface is rough, or if the sealing lip is scratched or otherwise damaged, the seal may leak. Furthermore, such straight bore metal seals are generally not stacked in series to increase reliability unless a cartridge or other carrier is provided to contain them. Such a carrier, however, adds additional cost to the seal, may create another potential leak path in the seal, and may necessitate enlarging the packing gland and packing chamber.
The present invention is directed to overcoming, or at least reducing, the effects of one or more of the problems set forth above.